1. Field of the Invention
This invention relates to the field of analysis devices for computer networks.
2. Background Art
A computer network is an inter-connected connection of autonomous computers. The computer network allows these computers to exchange information and share resources (i.e., files, printers, modems, storage units, etc.). The network is made up of hosts (e.g., computers) connected by a communications subnet. The subnet consists of transmission lines and may include switching elements. The subnet may be one of two types, namely, broadcast type or point-to-point type.
Broadcast systems have a single communications channel that is shared by all the machines on the network. When a message (also known as a "packet") is sent on the broadcast system, all machines receive the packet. An address field within the packet specifies the destination machine. If the destination address does not match a particular machine's address, the machine ignores the packet. When the address matches the receiving machine's address, the packet is received.
A point-to-point system typically involves a number of hardwire transmission lines, each one connecting a pair of switching elements or hosts. One standard for utilizing a point-to-point system subnet is known as a "token ring" system (IEEE standard 802.5). Ring networks have many advantages. A ring system is substantially digital, improving communications, reliability and integrity. A ring also has a known upper limit for channel access and has limited contention problems.
In a token ring network, a special bit pattern, known as the "token," circulates around the ring. When a station wishes to transmit, it "seizes" the token, that is, removes it from the ring. That station is then free to transmit a packet. Because there is only one token on the ring, only one station can transmit at a time, eliminating contention problems. After the message has been propagated around the ring, the sending station removes it from the ring. After the message has been removed, the sending station retransmits the token so that another station may send if desired.
It is highly desirable to monitor the performance of an installed token ring network. By monitoring parameters such as physical ring delay, token rotation, bandwidth utilization, and others, a network administrator can optimize utilization of the network, identify and locate problems and plan expansion. The information generated from on-line analysis and monitoring permits trouble-shooting by the network administrator as well.
In the prior art, network monitors have been limited to monitoring "conversations," that is, packet data transmissions. These systems function only at the mid and upper levels of the network hierarchy. One disadvantage of these prior art monitors is the inability to capture all information transmitted on the network. For example, prior art systems do not capture tokens, token aborts or other low-level information. This prevents the generation of accurate utilization data. Another disadvantage is a reliance on the host or switching station for intelligence. This burdens the processing power of the host and limits the performance of the monitor.
Typically, prior art monitoring schemes utilize existing hardware designed to implement the network protocol. Because the heart of these prior art monitors are designed for a different purpose, the monitor is not able to execute desired monitoring functions. It is desired to have a network monitor which can function at each level of the network hierarchy, obtain all transmitted messages, permit simulations and utilization analysis.
Therefore, it is an object of the present invention to provide a method and apparatus for network monitoring which provides for complete data capture.
It is another object of the present invention to provide a method and apparatus for network monitoring which can operate at all levels of the network hierarchy.
It is still another object of the present invention to provide a method and apparatus for network monitoring that permits simulation of network activity and generation of controlled amounts of traffic.